The present invention relates to an actuator for a machine, especially an excavator, with at least one supply port and one working port and with at least one hydraulic accumulator.
Actuators for machines are readily available on the market in a plurality of embodiments. The supply port is used to connect a pump unit, for example, in the form of a hydraulic pump, to supply the hydraulic circuit connected to the working port with pressurized hydraulic fluid. These hydraulic circuits are generally divided into a high pressure part and a low pressure part. The actuating means for the machine is connected to the low pressure part through which low pressure part the operator, for example, the excavator operator, actuates the equipment of the high pressure circuit for working processes. A hydraulic accumulator ensures hydraulic supply for a certain interval in case of a supply failure within the hydraulic circuit to prevent the working equipment, for example, in the form of a drag, from falling down in the raised state or the like. This falling would constitute a safety risk.
In the known or conventional actuators, the hydraulic accumulator must first be charged to produce this safety function. To ensure emergency supply, the machines they cannot immediately begin working. Rather, a defined actuation function must first be carried out by the excavator operator, for example, by lifting the drag, to guarantee that the accumulator in this process is charged for a later emergency function. Generally, this working process is described in the operating instructions of the machine and must be carried out with the corresponding accuracy.
A generic actuator for a machine is disclosed DE-A-30 34 467, and monitors a connection between a supply port and a storage tank (tank T) on one side and a hydraulic accumulator on the other side. A relay valve has a valve element impactable by the pressure in the hydraulic accumulator, and a switching valve controllable by the relay valve. The valve element of the relay valve optionally connects a control line leading to the switching valve with the supply port or the storage tank (tank T). The known actuator promotes reliable on and off switching of the hydraulic accumulator. The valve element of the relay valve does not assume a control function, i.e., the connection between the hydraulic pump and the hydraulic accumulator is either completely open or completely closed. During reversing from pump pressure to accumulator pressure and vice versa, the valve element completes a rapid switching motion and hence acts like a flip-flop connection. This arrangement results in reliable on and off switching of the hydraulic pump and the storage tank (tank T) and/or the respective consumer. Realization of emergency supply within the meaning outlined above is, however, not possible with the disclosed actuator, which merely ensures a monitoring function.
Objects of the present invention is to provide improved actuators to ensure an emergency function before the machine begins to perform work.
The pressure prevailing in a secondary line and corresponding essentially to the fluid-side accumulator pressure is used for switching the switching valve. Because of a pressure reducing valve being situated between the switching valve and the secondary line, the pressure reducing valve separates within a hydraulic circuit a low pressure part from a high pressure part. Both parts are supplied via the supply port. The high pressure circuit is separated from the supply port and moreover from the supply circuit. The hydraulic accumulator is charged via the supply port when the machine is turned on, before the machine begins to perform work. Thus, immediately after the drive assembly and moreover the hydraulic pump are turned on, emergency supply pressure is available. The operator can immediately begin working without needing first to consider the emergency function. This arrangement enhances safety and facilitates operation of the machine, and therefore, guarantees immediate operating availability. Separation of the supply port from the working port can be complete in the sense of fluid blocking. Preferably, there is only partial separation, for example, by means of a choke which can still ensure partial supply of the high pressure circuit for certain working functions, at the same time emergency supply being ensured.
Furthermore, supply of the high pressure part as well as the low pressure part can be ensured by only one supply port. In contrast to optional electric control of the switching valve by electric switching magnet, the actuation of the switching valve is pressure controlled and hence functionally reliable.
In another preferred embodiment of the actuator of the present invention, between the switching valve and the secondary line, a pressure reducing valve is within a hydraulic circuit to separate the low pressure part from the high pressure part. The two parts are supplied via the a supply port. In this way, supply of the high pressure part and the low pressure part can be guaranteed via only one supply port.
In another preferred embodiment of the actuator of the present invention, between the secondary line and the hydraulic accumulator, a return valve opens in the direction of the hydraulic accumulator ensuring therethrough reliable separation in the case of supply failure, especially of the pump flow, from the low pressure part to the high pressure part. Preferably, the hydraulic accumulator with its fluid side is connected to the low pressure part which supplies the control unit, especially with a joystick, via another valve, especially a sliding valve. The control unit, as part of the actuating means of the machine, is thus supplied via the fluid side of the hydraulic accumulator and can influence the low pressure part with the equipment connected to it via corresponding control units.
In another preferred embodiment of the actuator of the present invention, the secondary line discharges into another working port. On the low pressure side, a third working port can be cut off via a third valve, especially in the form of another sliding valve. In this way, within the actuator still other working ports are available for actuating processes on the machine. Preferably, the sliding valves, the pressure limitation valves and the pressure reducing valves are connected to a tank port having essentially the ambient pressure.
In one especially preferred embodiment of the actuator of the present invention, the hydraulic accumulator is a membrane accumulator. The hydraulic accumulator and all the valves are made as screw-in parts, especially in the form of screw-in cartridges. Preferably, the actuator is made in a block design, the actuator block on the outer periphery side being provided with the supply port, the working ports and the tank port and with connection points for accommodating the screw-in parts. Within the actuator block, the connecting lines preferably extend between the ports and the connection points. In this way, a modular structure of the actuator concept is accomplished, with a compact structure requiring little installation space within the machine. Furthermore, when one component fails, it can be easily and economically replaced by a replacement part. The reversing valve and the return valve are preferably made as kits.
Preferably, the low pressure part has a working pressure of at least 20 bar, and the high pressure part has a working pressure of at least 200 bar.